The first five Iridium satellites were launched on May 5, 1997, and by 2002 there were 66 operational satellites, providing consistent global satellite phone coverage. These satellites have the interesting property that their antenna panels sometimes reflect sunlight down to the Earth’s surface, causing what came to be known as “Iridium flares”, delighting terrestrial observers—myself included. During an Iridium flare event, the satellite suddenly appears and gradually brightens and then dims to invisibility as it moves slowly across a section of sky over several seconds. Many of these events reach negative magnitude, with some getting as bright as magnitude -9.5.
The next generation of Iridium satellites began launching in 2017, but these satellites are constructed in such a way that they do not produce flares. Gradually, the original Iridium satellites are de-orbiting (or being de-orbited), so eventually there will be no more Iridium flares.
The Iridium flares haven’t been much of a nuisance to astronomers because the number of events per night for a given observer have been in the single digits.
But now we’re facing too much of a good thing. The first volley of 60 Starlink satellites was launched on May 24, with 12,000 expected to be in orbit by 2028. These satellites will provide broadband internet service to the entire planet. Though the Starlink satellites aren’t expected to produce spectacular flares like the first generation of the Iridium satellites, they do reflect sunlight as any satellite does, and the sheer number of them in relatively low Earth orbit is sure to cause a lot of headaches for astronomers and stargazers throughout the world.
I estimate that about 468 of the 12,000 satellites will be above your horizon at any given moment, but how many of them will be visible will depend on their altitude (both in terms of distance above the Earth’s surface and degrees above the horizon), and where they are relative to the Earth’s shadow cone (they have to be illuminated by sunlight to be seen).
And Starlink will not be the only swarm of global broadband internet satellites, as other companies and countries plan to fly their own satellite constellations.
This situation illustrates yet another reason why we need a binding set of international laws that apply to all nations and are enforced by a global authority. The sooner we have this the better, as our survival may depend upon it. How else can we effectively confront anthropogenic climate change and the precipitous decline in biodiversity?
As for these swarms of satellites, two requirements are needed now to minimize their impact on astronomy:
- Build the satellites with minimally reflective materials and finishes
- Fly one internationally-managed robust constellation of global broadband internet satellites, and require competing companies and nations to utilize them, similar to the co-location often required for terrestrial communication towers
I’d like to close this piece with a few questions. Will future “stargazers” go out to watch all the satellites and generally ignore the real stars and constellations because they are too “boring”? Will professional astronomers increasingly have to move their operations off the Earth’s surface to the far side of the Moon and beyond? Will we continue to devalue the natural world and immerse ourselves ever more deeply into our human-invented virtual environments?
5 thoughts on “A Shroud of Satellites”
In case you were wondering how I estimated 468 satellites of the 12,000 Starlink satellites would be above your horizon at any given moment, here’s what I did.
(1) Satellites are uniformly distributed around the Earth.
(2) The percent of the Earth’s surface visible from a satellite orbiting at an altitude a above the Earth’s surface also gives you the percent of the sky (i.e. surface area) you can see at that altitude from any point on the Earth’s surface.
Percentage of Earth Visible for Given Altitude
SpaceX Launches First Volley of Starlink Satellites – Bob King
The International Astronomical Union issued the following statement about satellite constellations on 3 Jun 2019:
And here is a before and after Starlink photo of Supernova 2019ein in NGC 5353, a galaxy in Canes Venatici:
The American Astronomical Society (AAS) issued the following position statement on satellite constellations on 10 Jun 2019:
From the AAS:
A report by experts representing the global astronomical community concludes that large constellations of bright satellites in low Earth orbit will fundamentally change ground-based optical and infrared astronomy and could impact the appearance of the night sky for stargazers worldwide. The report is the outcome of the recent SATCON1 virtual workshop, which brought together more than 250 scientists, engineers, satellite operators, and other stakeholders.
Live updates on large satellite constellations from the AAS: